bConsider a manufacturing process depicted by the following flowchart.

flowchart

Station A has $3$ parallel operators, A$1,$ A$2,$ and A$3.$ Station C has $2$ parallel operators, C$1$ and C$2.$ Each unit only needs to be processed by one of the operators A$1,$ A$2$ and A$3.$ After being processed at Station B $($with a single operator$),$ a unit then needs to be processed by either C$1$ or C$2.$ The process time of the individual operators are given as follows.

A$1,$ A$2,$ and A$3$: $21$ minutes

B: $14$ minutes

C$1$ and C$2$: $2$ minutes.

The process initiates the production of a new unit every $28$ minutes. What is the labor productivity $($in units$/$hour$)$ of this process?

Note: $1.$ Round your final answer to $2$ decimal places if it is not a whole number.

$2.$ Operators are paid even if they are idle.